25 replies to this topic

[Nev]

I find all this stuff fascinating, I wish I had a formal education in it really, though now-a-days most of this sort of thing is all (extremely expensive) software designed I expect.

 

"Rubbage" is a well known engineering term (in my garage at least!)

[vxah]

Nev, I thought you built "Nipper"? I seem to recall you looking into turbo a/r ratio's and stuff... Did you build the bottom end with stock dimensions and did you not look at changing rod length etc?

 

[Nev]

Nev, I thought you built "Nipper"? I seem to recall you looking into turbo a/r ratio's and stuff... Did you build the bottom end with stock dimensions and did you not look at changing rod length etc?

 

 

The square bore of a Z20LET seemed fine to me at the time and also a change like that would have introduced a little more risk to what was already a risky engine build. If anything, maybe a shorter throw might have helped promote power to the top end and allow more RPM, but the weak point is the oil pump as it's gear can shatter and also I didn't know the point that it might cavitate at.

 

I've set my hard RPM limit to 8000, though a couple of other Z20LEx owners have taken it up to 8250 and 8500 with their square bores (86mm).

 

 

 

[Ormes]

I find all this stuff fascinating, I wish I had a formal education in it really, though now-a-days most of this sort of thing is all (extremely expensive) software designed I expect.

 

 

Wish I'd trained in mechanical engineering and/or fluid dynamics or some such.

[Exmantaa]

If you search the net you will find a lot of pro/con stories about the perfect R/S ratio and it's effect on low or mid/high torque, but in the end there are far more important engine specs for it's power output then this ratio. So simply fit what crank/rod/piston combo is available for the engine. 

Edited by Exmantaa, 26 January 2017 - 08:59 PM.

[fezzasus]

 

 

What dose any of that mean ?????? are these parts easy to source in the uk ? will any of them fit into a z22se will I need to do other stuff if I should use any of those bits for an engine rebuild.? yes I know I know bugger all but I'm trying to learn.

 

What this means really is that the period of time a piston spends at tdc/bdc is dependant on the length of the connecting rod relative to the crankshaft stroke. So, with a short rod length as the crank swings around tdc the angle of the rod will change dramatically causing the piston to move in the bore added to the actual mechanical stroke change, this gives a faster piston acceleration/deceleration which can be an advantage or disadvantage depending on other factors of the engine design, like a fast acceleration could be good for large intake ports to get the air moving early?

However there are other issues like the extra side loading on the piston/bore due to the angle of the rod on the power stroke plus extra forces on the piston due to the increased speed changes at higher rpm..

 

Does that help at all...  

 

 

I think the side loading/friction on the pistons is a key thing. Apparently (from what I've read (page 11 of this: http://hpwizard.com/...Lubrication.pdf)) around 50% to 75% of engine losses are due to the piston friction, of which the rings are around 20%. Thus the more the rock/twist in the cylinder (due to short rods) would imply more and more friction from the piston side walls.

 

I've seen how worn out the skirts were on several sets of Z20LET pistons and it's clear there is a lot of rubbage on them.

 

 

 

That's a massive generalisation and doesn't hold true for peak power. The oil pump begins to dominate friction at higher RPM